The present invention relates to a storage battery and relates, in particular, to a lead-acid storage battery that requires stable cycle life characteristics over a wide range of environmental temperatures.
When a lead-acid storage battery is subjected to repeated operations of charge and discharge cycling, the active material of the battery""s negative electrode is contracted due to changes in volume of the active material that take place at charging and discharging times. The rate of contraction of the active material is different between the interior and the surface of the active material layer and, therefore, repeated operations of charge and discharge cycling cause the active material to deteriorate in reaction in the inner layer thereof, thereby reducing the capacity of the negative electrode. As a result, life is shortened to create a problem.
In order to prevent the above from occurring, it is proposed that such anti-contraction agents as an organic expander including lignin and the like are added to a negative electrode""s active material, thereby achieving enhanced cycle life. According to a prior art structure, however, repeated operations of charge and discharge cycling result in dissolving of an organic expander such as lignin and the like, not allowing to perform the function of an anticontraction agent for a long period.
Therefore, the negative electrode capacity has declined, thereby presenting a problem of shortening battery life. This shortening of battery life is accelerated by operating at elevated temperatures. Thus, life characteristics at high temperatures have been extensively jeopardized when compared with the life characteristics at room temperature.
In recent years, a great deal of efforts has been made on the development of batteries for electric vehicles, wherein many batteries are installed in a limited space and further a high rate of charge and discharge cycles takes place, thereby causing the battery temperatures to be liable to increase. To prevent the batteries"" degradation at such high temperatures has been a significant challenge to the industry.
A storage battery of the present invention comprises an electrode and an electrolyte material, in which the electrode has a grid with each respective mesh measuring about 50 mm2 or less in area, and an active material that is provided on the foregoing grid.
According to the construction as described in the above, it is made possible to prevent a reduction in the negative electrode""s conductivity caused by a contraction of the negative electrode active material that takes place noticeably when a charge and discharge cycle is repeated, especially at high temperatures.